Two Missouri women accused of using antifreeze to fatally poison two family members and attempt to kill a third will continue to be held without bond until their preliminary hearing next month, a Greene County judge has ruled.

Both Diane Staudt, 51, and her daughter, Rachel Staudte, 22, are charged with two counts of first-degree murder, one count of first-degree assault and one count of armed criminal action. They appeared in court Monday, where they waived a reading of the charges and entered not guilty pleas.

The two are accused of poisoning Diane Staudte's husband, Mark Staudte, 61, who died in April 2012, and her son, Shaun Staudte, 26, who died five months later.

"It's a very unusual case, not only for what we see in Greene County, but also what you see across the country, when you have a family member killing off other members in that manner," assistant Greene County prosecutor Todd Myers said.

Springfield police received an anonymous tip June 11 that Diane Staudte was possibly responsible for two or three homicides and the hospitalization of her daughter, Sarah Staudte, 24, according to court documents.

On June 9, Diane Staudte posted a comment on her Facebook page asking for prayers for her daughter, Sarah, who was in critical condition in an intensive care unit.

A Springfield police investigator went to the hospital June 13 and was told by the nurse in charge of Sarah Staudte's care that her condition was potentially fatal and that doctors didn't know what was wrong with her, a probable cause statement says.

The nurse described Diane Staudte's behavior during a few short visits with her daughter in the hospital as "inappropriate," saying the mother "was aware Sarah's condition was life-threatening" but "made jokes and laughed with hospital personnel."

According to the probable cause statement, Diane Staudte told investigators Thursday that she poisoned her husband with antifreeze because she hated him, and killed her son because he was "worse than a pest." She also admitted poisoning Sarah Staudte over four days because "she would not get a job and had student loans that had to be paid," investigators said.

Sarah Staudte is expected to survive but could have permanent damage from the poison, the hospital told investigators.

Diane Staudte initially took complete blame for all three poisonings, but the next day Rachel Staudte admitted to police that she had been involved in them, as well.

The public defender appointed for Rachel Staudte declined to comment Tuesday, while Diane Staudte's attorney wasn't immediately available for comment.